Comment # 11 on bug 109239 from Samuel Pitoiset

FWIW, it's not a cable issue, I tried to replace it, same problem.

Though, after trying with a new 4K screen the problem is "fixed".

I assume it's a screen issue, I also tried to reset settings to default for the 
old screen but the problem still occurs.

Do you need more info about that screen?

Keep in mind that the problem doesn't happen with amdgpu.dc=0 on Polaris10.